The long-range goal is to understand the adult myofiber pattern in the human heart and its morphogenesis and to relate this understanding to the contractile and conductive properties of the heart. The work builds on our experience gained in reconstructing the global myofiber patter. Specific aims are to : a) establish the myofibre pattern in the fetal, neonatal and adult heart; b) establish the pattern in the embryonic, neonatal and adult heart and c) to build a mathematical model of myofiber morphogenesis in hearts. In addition the myofiber pattern in asymmetric septal hypertrophy (where the normal pattern is know to be disrupted) will be studied in infant and adult hearts. The basic methodology utilizes embedding of whole hearts, emplacement of fiducials, serial sectioning, semiautomated photomicrography, manual digitization, automatic coordinate reassembly, interactive 3-D computer graphics reconstructions, graphics file editing, image production and archiving. Software to support interactive morphometrics on the 3-D displays is to be implemented in the near future. The basic methodology just summarized is varied to suit the size of the heart. Small hearts are embedded in toto, sectioned and submitted to 3-D reconstruction. Large hearts are serially sectioned at 1 or 2 nm on a macrovibratome or 'minitome' and photographed to produce macroscopic reconstructions. Small tissue samples are then excised systematically from individual tissue slices, embedded, sectioned in toto and submitted to 3- D reconstruction. In this way the myofiber pattern is reconstructed systematically in large or small hearts. The application of this methodology will lead to the first global description of the myofiber pattern and its morphogenesis in the mammalian heart The results will improve our understanding of the architecture of the normal hart and of certain cardiac abnormalities.